Semiconductor devices such as diodes and transistors, for example field-effect controlled switching devices such as a Metal Oxide Semiconductor Field-effect Transistor (MOSFET) or an Insulated Gate Bipolar Transistor (IGBT) have been used for various applications including but not limited to use as switches in power supplies and power converters, electric cars, air-conditioners, and even stereo systems. Particularly with regard to power devices capable of switching large currents and/or operating at higher voltages, low on-state resistance, which is in the following also referred to as on-resistance Ron, soft switching behavior and high voltage blocking capability are often desired.
Edge-termination structures such as field plates and/or floating guard rings are often used in a peripheral area surrounding an active area for switching and/or controlling a load current to redistribute the electric field such that the electric field close to a semiconductor surface is reduced. Accordingly, blocking capability of the semiconductor device is improved.
In addition, higher doped field-stop regions may be used in power semiconductor devices to improve softness during switching-off and/or commutating the semiconductor device. Field-stop regions may be formed only in parts of the semiconductor device. Such field-stop regions could be formed by masked implantation, for example by proton implantation, and subsequent drive-in. For a typical power semiconductor device, the penetration depth of the field-stop region may, for example, be about 30 μm to about 60 μm. However, masking protons with high enough energy to penetrate deep enough into the semiconductor material typically poses significant challenges, in particular in thin-wafer technology. Using of apertures such as stencil masks is not compatible with thin-wafer technology. Forming thick masks on the wafer backside may cause significant wafer bowing. This may have an impact on the manufacturing. Thinner implantation masks may be used for other n-type dopants such as selenium or phosphorus. However, the related drive-in processes are accompanied by higher temperature loads which limits the use in thin-wafer technology.